The present invention relates generally to clutches, and more particularly to viscous clutches.
Viscous clutches are used in a wide variety of automotive fan drive applications, among other uses. These clutches typically employ relatively thick silicone oil (generally called shear fluid or viscous fluid) for the selective transmission of torque between two rotating components. It is possible to engage or disengage the clutch by selectively allowing the oil into and out of a working area of the clutch located between input and output members (e.g., between an input rotor and an output housing). A valve is used to control the flow of the oil in the working area between the input and the output. Recent clutch designs have been employed that allow the oil to be stored in the rotating input portion of the clutch while the clutch is disengaged, in order to keep kinetic energy available to the oil to allow rapid engagement of the clutch from the off condition. This also allows the clutch to have a very low output speed (e.g., fan speed) while the valve is positioned to obstruct oil flow into the working area. It has also become common for the clutch to be controlled electrically. This has been done to increase the controllability of the clutch, and to also have the clutch capable of responding to multiple cooling needs in a vehicle. Some of the possible cooling needs are coolant temperature, intake air temperature, air conditioning pressure, and oil temperature.
However, the electric control of a viscous clutch requires extensive effort to develop a desired control algorithm that governs clutch response to operational parameters. A separate control algorithm may be needed for every application, even where the basic clutch geometry remains the same.
Therefore, it is desired to provide an alternative viscous clutch.